QUALITY SCANNING:
Creating high quality scans for raster to vector conversion
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Resolution
It is not true that "the higher the scanner resolution, the better the vectorization results". In fact, a high resolution scan can sometimes give you worse raster to vector results than a low resolution scan!
That said, you should be aware that while you can decrease the resolution of an image after scanning you cannot increase it. Increasing resolution after scanning will not regain any lost detail. It will simply exacerbate "steps" in the image that will decrease the quality of any raster to vector conversion.
Therefore, it is better to err on the side of too high resolution rather than too low resolution when scanning. If you find your scan resolution is too high you can always decrease it after the fact.
For most drawings, a scan resolution of 200 to 400 dpi is optimal. Here are some pointers to look out for:
When resolution is too low, breaks often appear in the drawing and text becomes illegible.
When resolution is too low, curves often look stepped instead of smooth.
Stepped
Smooth
When resolution is too low, text characters and entities that are close together become joined.
Joined
Separated
(Note that the separation of close together entities is dependent on selecting an appropriate threshold as well as on selecting an appropriate resolution.)
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Q&A: ASK AN EXPERT
Q: Can you recommend a scanning bureau?
A: Please click here for a list of scanning bureaus.
Be aware that scan quality varies enormously from one scanning bureau to the next. You may get good quality scans from one bureau and utterly useless scans from another.
In our general experience, the majority of scanning bureaus are more likely to give you a mediocre scan than a top quality scan suitable for archiving and or automatic raster to vector conversion.
Yes, there are good scanning bureaus. The best ones take time and pay attention to the individual detail of each drawing. For them there is no "one size fits all" scanning solution. Because they take greater care to provide you with a quality end product they generally charge more for their personalised services.
Of course, there are some who will charge you as much as they can whatever the quality of their work!
NOTE: Avoid scanning bureaus who quote low (in order to get the work) AND WHO ALSO promise fast turn-around times. They maximise their profit by scanning your job as fast as they can. Too fast in our view! Their priority is to "get it finished ASAP!".
Of course, you can stipulate a reasonable deadline to reduce some of the pressure on them to "bang out the work" but, in our experience, most of these operators will continue to do it as fast as they can because that's the business they're in - low-cost, high volume scanning.
Some scanning bureaus have little or no knowledge of CAD or raster to vector conversion. Few care about the finer intracacies of scanning.
If you are serious about scanning and preserving your legacy data for posterity or for raster to vector conversion, don't accept the first quote you get. Choose those who stress scan quality first and price second.
It is reasonable to expect that a sample scan will show you the quality of work you can expect to get. Unfortunately, this may be the only scan a dodgy operator will put any effort into getting right. Worse, they may also use the settings from this scan as the basis for the rest of your job, the assumption being that all your drawings are the same. They seldom are. On interrogation drawings have many differences between them!
On a big job the worst offenders will use the same pre-determined settings on every scan. They will not interrogate each scan to see if it can be improved in any way by adjusting the settings. They will automatically save each scan with an unhelpful, incrementally updated file name, like "scanarch01", "scanarch02", etc. What they don't see, you get!
Caveat emptor, CAD user!
A good quality scan will generally take longer and cost you more.
We're happy to answer questions! Click here to email us.
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